1. Field of the Invention
This invention relates to a communication system and more particularly to a communication system which uses a distribution of propagated energy over a wide frequency spectrum in a manner such as to obtain reliable operation while minimizing interference with propagation of other signals. The system is readily implemented through the use of digital circuitry and is otherwise readily and economically manufacturable.
2. Background of the Prior Art
My aforesaid U.S. Patent issued Oct. 8, 1991 discloses a communication system in which wavetrains are propagated from a transmitting point to a receiving point, each wavetrain comprising a sequence of alternations having predetermined varying durations and propagated in a predetermined distinctive order. Energy received at a receiving point is sampled at sampling times having durations and an order corresponding to the predetermined varying durations of the transmitted wavetrains.
Important features of the invention disclosed in my said patent relate to the use of digital circuitry for establishing the durations and sequence of the propagated wavetrains and also of the sampling operation, to synchronization of sampling at the receiving point with the generation of the propagated wavetrains and to provisions for simultaneous transmission on a plurality of channels.
The system of my said patent is a spread spectrum system in that the propagated energy is in effect spread or distributed over a substantial range of frequencies, rather than being concentrated in a relatively narrow range of frequencies, as in the case of conventional AM and FM systems. Many other spread spectrum systems have been known or proposed, including direct sequence systems in which the phase of a carrier is controlled by a code sequence, frequency hopping systems in which a carrier frequency is shifted in accordance with a code sequence, pulsed-FM or "chirp" systems in which the frequency of a carrier is periodically swept over an interval of time, time hopping systems in which a carrier is transmitted at times determined by a code sequence and hybrids of two or more of such direct sequence, frequency hopping chirp and time hopping systems. Many of such systems have substantial success but in general they are complex, expensive and not always reliable.